With the increased propagation of silver halide photographic materials, it has been required to obtain photographs of high image quality with uniform finished quality quickly, easily and at high photographing successfulness.
In general, it is known that for a high-speed photographic light-sensitive materials for photographing, a silver iodobromide photographic emulsion having a mean silver iodide content of from about 4 to 20 mole %. A silver iodobromide emulsion having, in particular, high silver iodide content is advantageous for obtaining high speed and images of high quality but, on the other hand, has difficulty in quickening of development processing and also specific techniques are required for obtaining the stability of latent images and excellent reciprocity law failure characteristics.
In general, a silver chloride, silver chlorobromide or silver iodochlorobromide emulsion having a high mean silver chloride content (e.g., 30 mole % to 100 mole %) being used for black-and-white photographic papers and color print photographic papers is advantageous for quickening photographic processing but has difficulties not only in high sensitivity, images of high quality, the progression of the gradation of development, and the inhibition of fog but also in the shelf life thereof, the stability of latent images formed, and the reciprocity law failure characteristics. Also, a silver halide photographic emulsion having a low mean silver iodide content of, for example, 0 to 4 mole % is advantageous for quick stabilization of desilvering in the case of using, in particular, for color photographic light-sensitive materials but has a difficulty in obtaining images of high quality.
It is known that the various characteristics of a silver halide photographic emulsion containing silver halide grains having (100) faces are totally improved by converting the emulsion into a corner development type silver halide (CDG) photographic emulsion using a CR-compound (i.e., a halogen conversion inhibitor or a chemical sensitization reaction inhibitor), preferably during or before the chemical sensitization step as described, for example, in Japanese Patent Application No. 311131/86.
A silver halide photographic emulsion containing silver halide grains having (111) faces is easily obtained in, mainly, a silver iodobromide emulsion and has various disadvantages as described above. Aforesaid Japanese Patent Application No. 311131/86 does not mention the solving method of the disadvantages of the photographic emulsions. A method of improving each disadvantage is proposed on normal crystal silver halide grains having the (111) faces, such as octahedral grains, tetradecahedral grains, tabular grains, tabular twin crystal grains, etc. However, a method of totally improving the properties of the silver halide photographic emulsions have not yet been proposed by the reasons of being influenced by other various factors outside object.
For example, such improvements are described in Japanese Patent Application (OPI) Nos. 147727/85, 99751/87, 162540/84, 147728/85, 153428/77, 155827/79, 95337/83, 113926/83, 133540/84, 82835/82, 108526/83, 48756/84, 210345/86, 26589/80, 196749/85, and 205929/86 (the term "OPI" as used herein means an "unexamined published patent application"), U.S. Pat. Nos. 4,434,226, 4,414,310, 4,433,048, 3,966,476, 4,414,306, 4,490,458, 4,413,053, and 4,183,756, and British Patent No. 2,038,792.
In particular, Japanese Patent Application (OPI) No. 108526/83 shows in Examples 6 and 7 thereof that according to an arrested development study, epitaxial silver halide grains, that is, silver halide grains formed by epitaxially joining silver bromide grains or silver chloride grains to the corner portions of tabular silver iodobromide grains having an aspect ratio of at least 8 as a host silver halide cause a development at the corner portions. However, neither the objects nor effects of the present invention are suggested therein.
Silver halide photographic emulsions containing silver halide grains having (111) planes and having, for example, a mean silver iodide content of from 0 to 4 mole % and a mean silver chloride content of at least 30 mole %, preferably at least 50 mole % are described in Japanese Patent Application Nos. 144228/86, 144229/86 and 47225/87. The photographic emulsions of such halogen compositions have a tendency of showing the aforesaid disadvantages as compared to ordinary silver iodobromide emulsions.
For photographic light-sensitive materials of a multilayer structure, in particular, multilayer color photographic materials, a stability is required not only on the sensitivity and gradation but also the exposure temperature, exposure time, latent images, development progress, etc., over all the layers and the stability gives crucial influences on the finished image quality of the photographic materials.
Furthermore, a developer for obtaining a sufficient sensitivity in a short period of time, a light-sensitive material excellent in developability and giving sufficient blackened density in a short period of time, and characteristics of drying in a short period of time after washing are required.
For improving the drying property of light-sensitive materials, there is generally a method of reducing the water content in the light-sensitive materials before initiating drying by previously incorporating a sufficient amount of a hardening agent (gelatin crosslinking agent) to the light-sensitive materials at coating step therefor to reduce the swelling amount of the emulsion layers and the surface protective layer(s) thereof at the steps of development, fixing and washing. According to the method, by using a large amount of a hardening agent, the drying time can be shortened the shorter but the reduction of the swelling amount of the photographic layers is accompanied by delaying of development, the reduction of sensitivity, softening of tone, and the reduction of covering power.
Moreover, in high-temperature quick processing by a developer and a fix solution having substantially no gelatin hardening action as described, for example, in Japanese Patent Application No. 292018/86, it is inevitable to sufficiently harden light-sensitive materials and in the case of using silver halide emulsions showing slow development progressing property, quick processing in a short period of time can not be realized.
On the other hand, a method of increasing the development activity of a developer is known and the amount of a developing agent and an auxiliary developing agent in the developer, the pH of the developer, and the temperature for processing can be increased.
However, these methods have such disadvantages that the preservability of the developer is reduced, the tone is softened although the sensitivity may be increased, and the light-sensitive materials are liable to be fogged.
On the other hand, apart from the view point of quick processing, the further increase of the sensitivity of light-sensitive materials and the improvement of graininess are a theme to be continuously persued.
If the sensitivity of a light-sensitive material is increased by increasing the grain size of silver halide grains of silver halide photographic emulsions for light-sensitive materials, the graininess is reduced.
Thus, it is necessary to obtain a high sensitivity with same grain sizes (in the case of tabular grains, the grain size is same as the diameter of the projected area thereof) or improve the graininess with a same sensitivity.
An object of this invention is to provide a silver halide photographic emulsion showing a very excellent development progressing property, sensitivity to fog ratio, and graininess and giving a high covering power in a tabular grain silver halide emulsion of a same diameter of projected area and same thickness.
For improving the view point as described above, techniques of utilizing tabular grain silver halide emulsions are described in U.S. Pat. Nos. 4,439,520, 4,425,425, 4,414,304, etc., but the object of the present invention relates to obtain the maximum performance of such tabular silver halide grains and provides far excellent performance thereof over those described in the aforesaid patents.
Also, Japanese Patent Application (OPI) No. 108526/83 discloses a technique of controlling the development initiating point by forming silver halide crystal (epitaxial growth) at a specific portion (for example, the top or center) of a tabular silver halide grain but such a technique is undesirable since the silver halide emulsion containing the silver halide grains reduces the stability thereof with the passage of time during when the emulsion is dissolved in water or is stored.
Furthermore, it is known as described in U.S. Pat. Nos. 3,628,969 and 4,225,666 that a spectral sensitization of a silver halide emulsion is performed simultaneously with a chemical sensitization by adding thereto a sensitizing dye and a chemical sensitizer at a same time and also it is known a described in Japanese Patent Application No. 113928/83 that a spectral sensitization of a silver halide emulsion can be performed prior to a chemical sensitization thereof and that a spectral sensitization of a silver halide emulsion can be initiated by adding thereto a sensitizing dye before finishing the precipitation of silver halide grains. Furthermore, it is known as disclosed in U.S. Pat. No. 4,225,666 that these sensitizing dyes are dividedly added to a silver halide emulsion, that is, a part of these compounds are added to an emulsion prior to the chemical sensitization thereof and the residue is added thereto after the chemical sensitization and also it is known as described in U.S. Pat. No. 4,183,756, etc., that the addition of the sensitizing dyes may be at any period during the formation of the silver halide grains.
However, these known techniques described above are yet insufficient.